When a splicing binding form occurs in a top-level context or
module context, its local bindings are treated similarly to
definitions. In particular, syntax bindings are
evaluated every time the module is visited, instead of only
once during compilation as in let-syntax, etc.

If a definition within a splicing form is intended to be local to the
splicing body, then the identifier should have a true value for the
'definition-intended-as-localsyntax property. For
example, splicing-let itself adds the property to
locally-bound identifiers as it expands to a sequence of definitions,
so that nesting splicing-let within a splicing form works as
expected (without any ambiguous bindings).